Open bottom ingot molds are supported on block slabs called stools, and are usually made of cast iron. These molds, which are from six to ten feet high have an open top through which molten steel is poured. They are conventionally of a rectangular shape and of decreasing cross-section from the bottom to the top of facilitate removal of the mold from the cooled metal ingots.
Due to variances during the manufacture of the molds and the stools, the bottom rim of the mold forming the joint between the rim and the stool is irregular. As the mold is used, these irregular areas erode under contact with the molten metal. As the joint between the mold stool and the mold rim loses integrity, the molten metal escapes the container and cools under the mold rim causing "ribs" or "fins" on the cooled ingot. Removal of the ribs or fins is necessary before further working of the ingot may be accomplished.
At the initiation of the pour, a crucible of hot molten steel is poured through the open top portion of the mold. The stream of molten steel dropping some six to ten feet inside the mold, hits the mold stool with considerable force splashing molten steel onto the sidewalls of the mold and causing a concave erosion of the stool surface. This erosion of the stool surface results in a convex bottom or "knob" on the ingot. This knob makes handling of the ingot difficult and prevents the ingot from standing totally upright in a soaking pit furnace and in other processing of the steel. As a result, the ingot may contact another ingot in the soaking pit or contact the pit wall causing damage to the furnace. In addition, the erosion of the stool frequently causes the ingot to become welded to the stool causing what is known as a "stool sticker".
The splashing of the molten steel on the sidewalls at the beginning of the pour continues until a sufficient amount of molten steel accumulates in the bottom of the mold to provide a cushion for the on-flowing stream. Because the walls of the mold are cold, the splashing steel often solidifies and oxidizes before the metal level in the mold reaches the splashed material. These oxidized particles form "scabs" which, like ribs, fins, or knobs, must be removed from the ingot prior to further processing.
In order to alleviate one or more of the foregoing problems, many splash shields, splash cans, joint sealers, mold shields, and the like have been proposed. One conventional method for providing a seal between the mold rim and the stool is to caulk the joint or erroded channels with a refractory material which is placed around the outside of the mold. This practice allows the formation of ribs or fins on the inside of the mold in spaces that are not completely caulked with the refractory material. In another method, refractory material or fiber is used to caulk the joint between the mold rim and the stool surface from the inside of the mold. The material can be combustible so that it is burned out by the molten metal. These caulking methods are labor intensive since the joint must be caulked entirely from inside the mold.
Another means of mold protection involves a so-called "splash can" or splash shield which is placed substantially flat along the wall of the mold to prevent scab formation on the ingot due to splashing as the mold is filled with molten material. In another method, a splash can or mold liner is a self-supporting, rigid structure which is inserted into the mold. The liner is consumable, and becomes an integral part of the formed ingot. An attendant drawback is that insertion of the liners in molds which have the "big end down" must be accomplished from the bottom opening of the mold.
Steel sheet material has also been used as mold guards. The metal sheet is placed interior the mold resting against one or more of the interior mold surfaces. The unattached sheets tend to migrate, shift or float from the turbulent action of the molten steel allowing the molten steel to "creep" between the shield and the mold.
It has been suggested that such shields or mold guards be fastened to the mold surface by means of bolts. This concept however, requires that threaded bores be provided in the interior wall. In installing such shields, the holes must be aligned and the bolts inserted. This procedure is labor intensive.